Process of making pancake or built-up sheet leather



y 6,1930. c. E. RAHR 1,756,993

PROCESS OF MAKING PANCAKEOR BUILT-UP SHEET LEATHER Filed May 29, 1925Patented May 6, 1930 UNITED STATES CHESTER E. RAHR, 0F BROOKLINE,MASSACHUSETTS, ASSIGNORTO. THE FLINTKOTE COMPANY OF BOSTON,MASSACHUSETTS, A CORPORATION 01 MASSACHUSETTS raocessor MAKING PANCAKEApplication filed May 29,

This invention relates to the manufacture of built-up sheet leather, orpancake so called, which may be employed in the manufacture of counters,heels, slip tops, and inner soles. Such sheet leather is generally. madeof scraps or trimmings of thin leather, sometimes called levellings,produced in splitting or skiving. leather to reduce it to a uniformthickness. The levellings are usually in sheets, varying in thicknessfrom that of a sheet of paper to of an inch, and may be of any shape.These levellings heretofore have been pasted together by flour anddextrine, or starch paste, in a pan or frame, to form a block or cake.The cake was then subjected to pressure, which forces out the greaterpart of the water, and was hardened by drying. The hardened cake isknown as built-up or pancake leather.

As-is quite obvious from the brief description given, one of the veryimportant factors entering into the production of pancake of goodquality is the character of the binder employed for pasting thetrimmings or levellings together. For example, in the manufactureof'counters from pancake, the paste should be of a quality to ensure astrong yet flexible counter. During the moulding of the counter, if theusual paste is too dry, and thus brittle, breaks inthe-back and heelflange of the counter may occur; while if the paste is in too wet acondition, a warped and illshaped finished counter will result after thedrying operation. Moreover, due to the use of binders which lose theirbinding properties under the action of water, pancake leather has beenused only in shoes of the poorest grades, and its wearing qualities werevery poor. In fact, due to the unsatisfactory characteristics of pancakeleather and to the high labor costs in itsmanufacture within recentyears, as well as because of the introduction of other and moresatisfactory substitutes, the manufacture of built-up leather of thischaracter has been decreasing.

The object of this inventionis to produce pancake leather which isstrong and yet flexible, which not disintegrated when subjectedto theaction of water, and which more closely simulates solid leather than theordinary pancake as heretofore produced. -ject, briefly. stated, isaccomplished by em- I ploying as a binder for the leather levellings: 4

0R BUILT-UP SHEET LEATHER 1925. Serial No. 38,827.

i This oba dispersion of'normally adhesive thermoplastic material,preferably asphalt This dispersion or emulsion may consist of an ad'hesive binder, such as asphalt, the asphalt being subdivided intominute or colloidal particles, and an emulsifying? agent suchi'ascolloidal'clay, the particles of asphalt beingprotected or enveloped bythe clay, and a liquid vehicle'or medium, such as water. The

emulsion may bemade by the process described in U. S. Letters Patent No.1,417,835,. granted May 30, 1922', to Lester Kirsch-- braum. Such asuspension or dispersion is non-adhesive, and may be made in paste orplastic form, so that itis capable of being spread or painted on thesurface of material.

With the elimination of'water by heat or by the action of heat andpressure, the asphalt particles coalescerand revert to their normallyadhesive and cohesive state, and on being thereaftersubjected to waterremain water:

proof and are not disintegrated. Pancake may be built up with such abinder and'yield a good product, superior to the heretofore commerciallyknown pancake. On the accompanying drawings Figure 1 represents more orless conventionally a somewhat enlarged section through a portion ofpancake leather just after it has v been made as hereinafter described.

Figure 2 is a similar view but shows the cake after it has been pressedand surfaceskived to a uniform thickness.

Figure 3 shows in perspective and more or less conventionally, forpurposes of illustration, a counter made with the finished prod- Beforebuilding pp the cake, the leather stock may, if desir be tempered orsoftened with water. The pancake may then be built in a frame. Theworkman starts by laying a sheet of thin leather that is cut somewhatlonger and wider than the frame, and covers it witha coat ,of bituminousemulsion, as by a paintin dipping or spraying operation. A layer ot 'thesmallr pieces of leather levellings is then distributed evenly overthempanca tire area of the frame, and coats of emulsion and layersofleather are laid alternately until the desired thickness of cake isobtained,-

The pressing may then be accomplished by a mechanical or hydraulicpress, by means of which heavy pressure may' be applied A layer of thesepancakes is placed on a steel plate and is covered, if desired, with asheet of burlap. Another steel plate is put on, then another layer ofpancakes and burlap, and so on until the press is filled. Pressure isapplied, and the greater part of the excess water in the cakesis pressedout and the cakes tight-1i compacted. The now firm but damp pressure inthe press,-as by heating the press, or ma be removed and hung up inasteamheate loft to dry. In either case, with the elimination of waterthe asphalt particles coalesce and become adhesive, binding the leatherlevellings together.

When dry, the pancake is hard and stiff, but

there is a certain amount of pliability and flexibility which isimparted to it by the coalesced asphalt particles, and'it is not asbrittle as the ordinary pancake as heretofore made. When tempered andsoftened in water before being worked, as for example, in the productionof counters, there is no tendency for the cake to disintegrate after itis in preper tempered condition, even after a prolonged soakin in water.The cake may be reduced to a uniform thickness as shown in Fig. 2, by asurface skiving machine, and may be cut into blanks for counters on adinking machine. One side of each blank is usually formed by the wholeiece of leather which forms the bottom of t e pancake, and theother,-which is the pieced side, is made up as the inside of thefinished counter. The blanks may be skived onthe pieced side and waxedon the outside, and then moulded into shape and the heel flange turned,thus completing the entire counter-forming operation, Figure 3illustrating a counter thus formed." The material may be freelytempered, because there is no tendency of the asphalt binder to bedisin-' tegrated by the moisture, and since the as- I no phalt possessa. certain amount'of flexibility,

the material is not subject to cracking as with the ordinary binders. v

When the hardened and dry cake is used for the manufacture of heels, itis cut into 'heel blanks by the usual cutting dies and built up. Theheel will be waterproof.

e may then be dried under heat and .It may be stated that by the use ofthe expression bituminous emulsion, as used in Y the appended claims Imean a suspension or dispersion in water of normally adhesive andcohesive bituminous material, preferably asphalti the particles ofasphalt being of minute or co by colloidal clay or other equivalentemulsifying or colloidal agent, the suspension or dispersion beinnon-adhesive and preferably in a pasty or p astic form, so that it maybe spread or painted on a surface. On the elimination of the water andon being subjected to heat and pressure, or both, the asphalt coa lescesand reverts to its normal adhesive and cohesive state.

By the term thermoplastic material, I mean any bituminous or pitchymaterial, such as natural and blown asphalts, stearin itches, or otherequivalent materials, so tenable when heated and possessingwaterproofing characteristics; and by the term colloidal or emulsifyingagent, I mean hydrophilic colloids, such as colloidal clay, soaps,sodium silicate, glue, gums, starch paste, and the like.

Having thus described an embodiment of this invention, it should beevident to those skilled in the art that it is susceptible of variouschanges and modifications without departing from its spirit or scope asdefined by the appended claims.

What I claim is:

1. A process of making built-up or pan cake leather from thin leather,which comprises applying a coating of a dispersion of a thermoplasticbinder in water to the surfaces of the thin leather and building up aplurality of layers of such coated leather tempered and softened by thewater component of said dispersion.

2. A process of making built-up or pancake leather from thin leather,which comprises applying a coatin or film of bituminous emulsion innon-a hesive form to the surfaces of the thin leather, building up aplurality of layers of such coated leather, applying pressure to thebuilt-up layers, and applying heat to coalesce the bituminous materialand to unite the layers.

3. A process of making built-u or pancake leather from thin scrap leater, which comprises applying a coating or film of a disloidal size andprotected or enveloped.

person of asphalt in water to the surfaces of l the thin leather,building up a plurality oflayers of such coated leather, and thendrycake leather from thin scrap leather, which comprises coating thesurfaces of such scrap leather with a dispersion of a thermoplastic vbinder containing water in the external phase,

building up a plurality of layers of such'co'ated leather tempered andsoftened by the water content of said dispersion, and then pressing andheating the built-up layers to remove the water and coalesce thepreviously dispersed particles of binder.

In testimony whereof I have affixed my signature;

CHESTER E. RAHR.

